Toothbrush Bristle With A Tapering Part and Toothbrush With Such Bristles

ABSTRACT

Bristle for a toothbrush, comprising a) a cylindrical part ( 1 ) with a maximum, constant cylinder diameter D zyl  and b) a tapered part ( 21 ) which adjoins the cylindrical part ( 1 ) and has a bristle end ( 3 ) and has an end face ( 4 ) which de-limits the bristle end ( 3 ), wherein the tapered part ( 21 ) tapers towards the bristle end ( 3 ); wherein the tapered part ( 21 ) has a length L of 10 mm or less and at least 3 mm; characterized in that the tapered part ( 21 ), at a distance X from the end face ( 4 ), which distance X is the same size as the cylinder diameter D zyl , has a diameter D of 95 to 140 μm, and a toothbrush with such bristles.

The present invention concerns a toothbrush bristle with a tapered part and a toothbrush containing such bristles.

Customary bristles suitable for toothbrushes exhibited a cylindrical cross section. Since such bristles had an insufficient cleaning performance in the interdental space and tended to injure the gingiva, it was begun in some instances in the nineties of the last century to provide the bristles with a pointed end (see e.g. EP-A-0 596 633). By virtue of the reduced diameter at the pointed end the cleaning performance in the interdental space improved; simultaneously the bristle became more flexible thereby, which lowered the risk of injury. On the other hand the cleaning performance on the tooth surfaces deteriorated.

In Korean patent KR 261658 (corresponds to U.S. Pat. No. 6,090,488) a toothbrush bristle with a tapered end was described, whereby the bristle had at the end of the tapering part a diameter of 0.04 to 0.08 mm. The tapered part of this bristle was thus not “pointed” anymore in the aforementioned sense. In the later EP-A-1 234 525 of the same inventor, however, a bristle with a tapered part is described in which the diameter at the end of the tapered part is now only 0.02 mm or less (this bristle therefore again resembles more the pointed bristles about according to EP-A-0 596 633). As the justification for having re-lowered the diameter at the end of the bristle the inventor states that the removal of calculus from periodontal pockets is difficult with the bristles of KR 261658.

The present invention seeks to provide an improved bristle with a tapered part.

The object set is achieved according to the invention by a bristle for a toothbrush, comprising:

a) a cylindrical part with a maximum, constant cylinder diameter D_(zyl); b) adjacent to the cylindrical part a first tapered part with a bristle end and an end face delimiting the bristle end, whereby the first tapered part tapers towards the bristle end; and c) an imaginary central axis which runs through the cylindrical part and the first tapered part and which pierces the end face at a piercing point; whereby the first tapered part has a length L of 10 mm or less and at least 3 mm, as measured on the central axis starting from the piercing point; Characterised in that the first tapered part has a diameter D of 95 to 140 μm, as measured on the central axis starting from the piercing point at a distance X being equal to the cylinder diameter D_(zyl).

Preferred embodiments can be derived from the dependent claims.

It was surprisingly found that the bristles according to the invention have a higher service life than the prior art pointed bristles: The tapered ends do, according to the finding of the applicant, bend over under the pressing force occurring during tooth brushing, which leads over time to a fatigue break of the bristle tip; this is avoided by the bristle ends which according to the invention are only tapered (not pointed). Simultaneously it was found that the bristles according to the invention are mechanically so stable that they have on the buccal tooth surfaces a cleaning performance, which is similar or even superior to the one of the cylindrical bristles. The bristles according to the invention are furthermore better suited for cleaning interdental spaces and approximal tooth surfaces than bristles with non-tapered filament ends, since the bristles according to the invention can reach approximal tooth surfaces better.

Preferably D is in the range of 100 to 130 μm, more preferably in the range of 100 to 125 μm. Also preferably the is first tapered part of the bristle has a diameter of 120 to 165 μm, as measured on the central axis at a distance of 1 mm starting from the piercing point, and a diameter of 90 to 135 μm at a distance of 0.1 mm, as measured in the same way.

The bristle according to the invention has essentially (or to the technically possible extent) a rotationally symmetrical shape around the central axis.

The profile line of the tapered part of the bristle (i.e. the diameter of the tapered part as a function of decreasing distance from the piercing point of the central axis through the end face) runs preferably in a monotonically declining way towards the end face. The term “monotonically declining” has in the context of the present application the usual mathematical meaning. More preferably the profile line of the tapered part is strictly monotonically declining in the mathematical sense.

The length of the tapered part (or, in the case of a bristle according to the invention bent in a U-shape and having two tapered parts, the length of both tapered parts) is preferably in the range of 6 to 10 mm.

The end face of the end of the first tapered part has at the said piercing point a surface normal which is preferably inclined by not more than 30° against the said central axis. This is generally automatically fulfilled if the end face has been formed by trimming of a pointed end (see herein below); it may also be brought about by a suited, rounding-off treatment of the end face and its edges which are adjacent to the mantle surface of the tapered part (see herein is below).

Three particularly preferred types of bristles according to the invention are as follows:

i) a bristle with a cylindrical part, to which is adjacent exactly one essentially rotationally symmetrical tapered part of a length of 10 mm or less (i.e. this bristle is analogous to a bristle being tapered on only one end);

ii) a bristle with a cylindrical part and exactly two essentially rotationally symmetrical tapered parts which are adjacent on opposing sides to the cylindrical part, each being of a length of 10 mm or less (i.e. this bristle is analogous to a bristle being pointed on both ends), in particular whereby the two tapered parts are essentially of the same profile, and

iii) a bristle with a cylindrical part, an essentially rotationally symmetrical tapered part of a length of 10 mm or less and an essentially rotationally symmetrical pointed end, whereby the tapered part and the pointed end are adjacent on opposing sides to the cylindrical part.

In all embodiments of the bristle according to the invention the edges, which may occur between the end face and the tapered part, may be removed by rounding off, as is customary for cylindrical bristles. The rounding off may be carried out by means of customary known processes, e.g. by using a grit paper.

Particularly preferred profile lines of the first tapered part are approximately according to the following profile tables 1 to 4. These indicate the diameters in function of the distance from the piercing point of the central axis through the end face (mean values with standard deviation from 6 specimens of each of these bristles). In the right outermost column of each table the maximal diameter of the cylindrical part (D_(zyl)) of the bristle is indicated. In line with the measuring definition for the diameter D of the first tapered part according to the invention each table also indicates at a distance X=D_(zyl) the corresponding diameter value. Furthermore the profile tables 1 to 4 also indicate the diameter values at a distance of 0.1 mm from the end face, in order to exemplify the preferred profile of the first tapered part near the end face.

profile 1 distance from the tapered end [mm] 0 0.1 0.202 1 2 3 4 5 6 7 8 9 10 diameter [mm] 0.107 0.113 0.117 0.147 0.172 0.183 0.190 0.195 0.197 0.199 0.201 0.203 0.202 (0.108) diameter range [+/− mm] 0.012 0.019 0.021 0.020 0.019 0.014 0.014 0.014 0.012 0.011 0.010

profile 2 distance from the tapered end [mm] 0 0.1 0.209 1 2 3 4 5 6 7 8 9 10 11 diameter [mm] 0.086 0.095 0.101 0.140 0.172 0.185 0.192 0.198 0.201 0.204 0.205 0.205 0.208 0.209 (0.089) diameter range [+/− mm] 0.012 0.018 0.021 0.018 0.015 0.013 0.010 0.009 0.008 0.008 0.007 0.006

profile 3 distance from the tapered end [mm] 0 0.1 0.209 1 2 3 4 5 6 7 8 9 10 diameter [mm] 0.096 0.101 0.104 0.127 0.151 0.170 0.183 0.191 0.199 0.202 0.206 0.208 0.209 (0.098) diameter range [+/− mm] 0.009 0.009 0.009 0.008 0.007 0.006 0.008 0.005 0.006 0.005 0.003

profile 4 distance from the tapered end [mm] 0 0.1 0.166 1 2 3 4 5 6 7 8 9 10 diameter [mm] 0.112 0.119 0.122 0.137 0.150 0.156 0.159 0.162 0.163 0.164 0.165 0.165 0.166 (0.117) diameter range [+/− mm] 0.010 0.011 0.009 0.009 0.008 0.008 0.007 0.007 0.007 0.007 0.007

It may happen that in some embodiments of the bristle according to the invention the diameter at the end face and at a small distance from the end face cannot be measured reasonably anymore. This is the case when the bristle end of the tapered part has been subject to a subsequent rounding off. This rounding off may in some instances bring about at the end of the bristle irregular and jagged shapes and uneven surfaces, which makes the direct measurement of the diameter near the end face impossible. It was now also surprisingly found for the bristles according to the invention that in these cases the diameter near the end face or at the end face may be determined approximately by a parabolic extrapolation, whereby the diameters of the bristle at distances of 1, 2 and 3 mm from the end face are taken as the support points for the parable. These support points are indicated in bold in the above tables. To prove that this works the above tables indicate at a distance of zero from the end face both the original, actually measured diameters of the bristle (as they were after trimming of the end but before the rounding off) and, immediately below in parentheses, the diameters determined by that extrapolation. The deviation between the actual diameter and the diameter determined by the extrapolation is minimal. Such a simple extrapolation is possible for the bristles according to the invention because the curvature of the tapered end is less pronounced than with the prior art bristles.

The bristles according to the invention consist of a plastic suitable for toothbrush bristles. They may preferably be, on the one hand, of a polyester, in particular of a polyester obtainable from a (C₂-C₄)-1,ω-alkylene glycol and terephthalic acid. More preferably the polyester is polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), and particularly preferred is PBT. On the other hand they may be of a polyamide, in particular of a polyamide obtainable from a (C₂-C₈)-1,ω-diamine and a (C₂-C₈)-1,ω-dicarboxylic acid; particularly preferred is here polyamide-6,6 (e.g. nylon).

For the production of the bristle according to the invention one may start from commercially available bristles being pointed on one end or on both ends, or from cylindrical bristles. At the time of filing the instant application producers of such bristles were e.g. Pragma, Shinyoung, Wessen, Hylon, Sogo, Best Whasung or Cheil Jedang.

Bristles according to the invention, which have exactly one first tapered part, may e.g. be obtained from a commercially available bristle being pointed on only one end by trimming of the pointed end, with simultaneous formation of the tapered end and the end face. In order for the overall bristle to have a length suitable for toothbrush bristles the other, cylindrical end of the bristle may be cut appropriately to size.

Bristles according to the invention which have, besides the first tapered part, either a second tapered part or a pointed part, may generally be prepared from commercially available cylindrical bristles of appropriate length by chemical etching of the ends to the suited tapered or pointed shape. This etching process has been known in the field of pointed bristles for a long time. Here again the tapered end may optionally be trimmed in order to achieve a useful overall length of the bristle.

On the other hand doubly pointed bristles are commercially available which only need to be appropriately trimmed on both ends in order to arrive at a bristle according to the invention having two tapered parts and having a length suitable for toothbrushes (see example 1).

In the chemical etching process the bristles may firstly be trimmed to a uniform length. Then they may be etched by immersing them perpendicularly into an etching liquor of typically 80 to 150° C. Examples for etching liquors are inorganic solutions, such as a strongly alkaline etching solution (e.g. a 25-50 percent by weight aqueous solution of NaOH or KOH) or a strongly acidic etching solution (e.g. a 60-98 percent by weight aqueous solution of sulphuric acid). Examples for etching liquors are also organic solvents such as m-cresol, trifluoroacetic acid, o-chlorophenol, trichlorophenol, DMSO, DMF and a mixture of phenol and tetrachloroethane. The duration of the immersion may typically be 10 to 20 minutes, whereby during this time the bristles may optionally be withdrawn gradually from the etching liquor at an arbitrarily chosen constant speed or speed which varies over time, whereby the profile of the etched end (i.e. the monotony of the profile line) may be influenced. After the etching the ends may be washed, depending on the etching liquor, with water, dilute base, dilute acid or a suited solvent at typically ambient temperature, and dried.

The etching conditions (type and temperature of the etching liquor, duration of the immersion) may on the one hand be chosen such that the diameter D of the tapered part is after the etching already within the range according to the invention, which is 100 to 140 μm. For this the etching is carried out for a shorter time than the etching of a prior art pointed bristle. On the other hand the conditions of the etching may be chosen such that firstly a pointed end is formed, which is then trimmed with obtention of the end face and the tapered part.

If desired the ends of the bristles may, after having been etched in an alkaline or acidic solution, additionally be trimmed before rounding off the ends. Whether the ends need to be trimmed may simply be determined by examining the state of the ends by means of a magnifying glass, after the ends have been taken out of the solution.

An object of the invention is also a toothbrush with bristles according to the invention. The bristles according to the invention may be inserted into the bristle carrier of a toothbrush in a way which is analogous to the way used for prior art single or doubly pointed bristles. Here, bristles according to the invention with two tapered parts or with one tapered part and a pointed part are preferably inserted into the bristle carrier in an U-bent shape using anchor plates. Bristles according to the invention with only one tapered part on the other hand are preferably inserted in an unbent shape into the bristle carrier using a process, which is known in the art as “AFT process” (anchor free tufting).

The invention is now further illustrated with reference to the example and figures, whereby in the figures

FIG. 1 shows a cross-sectional view of a bristle according to the invention, whereby the measuring parameters essential to the invention are also indicated;

FIGS. 2, 3 and 4 show three embodiments of bristles according to the invention; and

FIGS. 5 and 6 show tests for in vitro cleaning performance on blackened, then TiO₂-coated teeth with bristles according to the invention and conventional cylindrical bristles.

EXAMPLE 1 Preparation of Bristles with Two Equal Tapered Ends According to Above Profile Tables 1 to 4

As the starting bristles were used four commercially available, doubly tapered bristles which were as follows:

trimmed at a To obtain the distance from profile of above starting bristles the end [mm] table No. Pragma 0.18 × 28 mm 2 1 033004 A-BBC Pragma 0.19 × 28 mm 1 2 033004 A-BBC Shinyoung 0.20 × 28 mm 2 3 Wessen 0.18 × 24 mm 2 4

Each of the starting bristles was trimmed at both pointed ends at the distances as indicated in the middle column of the above table. The ends of the tapered parts of the bristles so obtained were rounded off with a TR89 Bristle Rounding Machine (manufactured by Tsujimura Co., Japan) using a grit paper of 240 mesh.

FIG. 1 shows an end with a tapered part of a bristle according to the invention. On the right side is shown the cylindrical part 1, the constant diameter of which simultaneously means the maximal diameter D_(zyl) of the bristle. Adjacent to the cylindrical part 1 is a tapered part 21, the tapering of which starts at a distance L from the piercing point 6 of the central axis 5 through the end face 4, and which extends in a strictly monotonically declining way to the end 3. The end face 4 of the end 3 is shown here after an idealized rounding off, i.e. in an approximately hemispherical shape; due to the trimming and subsequent real rounding off this end face could as well be rather planar, but with more or less is irregular or jagged edges. Also shown is that the diameter D which is essential for the invention is measured at a distance X from the piercing point 6, whereby the distance X is equal to the said maximal diameter D_(zyl) of the cylindrical part.

FIGS. 2-4 show three bristles according to the invention. In all these figures the bristle is shown bent in an U-shape, in which shape the bristles particularly of FIGS. 2 and 3 would be inserted into the bristle carrier of a toothbrush. The bending over is done in the cylindrical part 1, which is then itself bent in an U-shape. FIG. 2 shows a bristle according to the invention with two tapered parts 21, 22; FIG. 3 shows a bristle according to the invention with a first tapered part 21 and a pointed end 7; and FIG. 4 shows a bristle according to the invention with only one tapered part 21, whereby the remainder of the bristle is formed of a cylindrical part 1. This latter bristle could, in deviation from FIG. 3, also be inserted in an unbent shape into the bristle carrier of a toothbrush head.

FIGS. 5 and 6 show tests for cleaning performances, which were obtained on blackened, then TiO₂-coated teeth. Tested were:

(A) Brushes with bristles according to the invention having two tapered ends, being rotationally symmetrical and which were inserted in an U-bent shape into the brush (see FIG. 2) having a bristle field with a height of 11.5 mm; the bristles had a maximal diameter D_(zyl) of about 0.21 mm and a diameter D at a distance X=D_(zyl) of about 0.104 mm (these bristles corresponded approximately to the profile exemplified in above table 3); and (B) Brushes with conventional cylindrical bristles which were inserted in an U-bent shape into the brush and which had a diameter D_(zyl) of 0.175 mm; the height of the bristle field was 11.5 mm. In these tests the teeth of a model of a sextant of an upper jaw (with three molars, three premolars and one cuspid) were firstly coloured black and then whitewashed in white with a TiO₂ paste (25 g in 75 ml 26% aqueous ethanol). After one standardised brushing step of 1 min duration with the bristle field to be tested and with an applied pressure weight of 250 g the fraction of the teeth surfaces, which had been cleaned from the TiO2 paste, was determined. This procedure was used in a standardised way for each of the bristle fields to be tested, using for each a horizontal, vertical and a rotatory cleaning movement, which procedure was repeated four times for each bristle field to be tested and each cleaning movement. In the horizontal cleaning (indicated in the figures with white bars) the standardised brushing step consisted of 60 forward and backward movements with an amplitude of 30 mm; in the vertical cleaning (indicated in the figures with hatched bars) it consisted of 60 upward and downward movements with an amplitude of 8 mm; and in the rotatory cleaning (indicated in the figures with dotted bars) it consisted of 60 circles with radius of 4 mm with simultaneous 16 horizontal forward and backward movements with an amplitude of 30 mm. The measured cleaning performances, i.e. the fraction of removed TiO₂, are indicated in the FIGS. 5 and 6 in arbitrary units.

FIG. 5 shows the sum of the mean values of the cleaning performances after horizontal, vertical, and rotatory cleaning movements with the bristles according to the invention (bar A) and with the conventional cylindrical bristles (bar B) on buccal tooth surfaces.

FIG. 6 shows the sum of the mean values of the cleaning performances after horizontal, vertical, and rotatory cleaning movements with the bristles according to the invention (bar A) and with the conventional cylindrical bristles (bar B) on mesial/distal tooth surfaces, i.e. on the tooth surfaces facing the interdental spaces.

It can be seen from FIG. 5 that the bristles according to the invention are, despite a lower mechanical rigidity, slightly better on buccal tooth surfaces with horizontal and vertical cleaning movements than the conventional bristles. It can be seen from FIG. 6 that the bristles according to the invention are clearly better than the conventional bristles in particular in the horizontal and vertical cleaning movements on mesial/distal tooth surfaces. 

1. A bristle for a toothbrush, comprising: a cylindrical part with a maximum, constant cylinder diameter D_(zyl); adjacent to the cylindrical part a first tapered part with a bristle end and an end face delimiting the bristle end, whereby the first tapered part tapers towards the bristle end; and an imaginary central axis which runs through the cylindrical part and the first tapered part and which pierces the end face at a piercing point: whereby the first tapered part has a length L of 10 mm or less and at least 3 mm, as measured on the central axis starting from the piercing point; wherein the first tapered part has a diameter D of 95 to 140 μm, as measured on the central axis starting from the piercing point at a distance X being equal to the cylinder diameter D_(zyl).
 2. A bristle according to claim 1, wherein D is in the range of 100 to 130 μm.
 3. A bristle according to claim 1, wherein the first tapered part has a diameter of 120 to 160 μm, as measured on the central axis at a distance of 1 mm from the piercing point, and has a diameter of 90 to 135 μm at a distance of 0.1 mm, as measured in the same way.
 4. A bristle according to claim 1, further comprising a second tapered part adjacent to the cylindrical part on a side opposed to the first tapered part.
 5. A bristle according to claim 4, wherein the second tapered part has essentially the same shape as the first tapered part.
 6. A bristle according to claim 1 further comprising a pointed end adjacent to the cylindrical part on the side opposed to the first tapered part.
 7. A bristle according to claim 1 characterised in that the cylinder diameter D_(zyl) is in the range of 150 to 170 μm or in the range of 180 to 210 μm.
 8. A bristle according to claim 1 consisting of polyester or a polyamide.
 9. A bristle according to claim 1, consisting of polyethylene terephthalate, polybutylene terephthalate or polyamide-6,
 6. 10. A toothbrush comprising one or more bristles, each bristle comprising: a cylindrical part with a maximum, constant cylinder diameter D_(zyl); adjacent to the cylindrical part a first tapered part with a bristle end and an end face delimiting the bristle end, whereby the first tapered part tapers towards the bristle end; and an imaginary central axis which runs through the cylindrical part and the first tapered part and which pierces the end face at a piercing point; whereby the first tapered part has a length L of 10 mm or less and at least 3 mm, as measured on the central axis starting from the piercing point: wherein the first tapered part has a diameter D of 95 to 140 μm, as measured on the central axis starting from the piercing point at a distance X being equal to the cylinder diameter D_(zyl). 